3 Mutations in Dna Lac operon DNA repair DNA/RNA/protein synthesis Start and stop codons Functional organization of a eukaryotic gene Regulation of gene expression

Question 1

Rank the following types of mutations from most to least severe: missense, frameshift, silent, and nonsense.

Answer 1

Frameshift > nonsense (a stop codon) > missense > silent

Question 2

What type of DNA mutation results in no change to the amino acid that is being coded for?

Answer 2

Silent mutation

Question 3

Silent mutations are often the result of changes in what position of a codon?

Answer 3

Missense mutation—the severity of the mutation depends on the location of the change

Question 4

What type of DNA mutation results in the misreading of all downstream nucleotides? Why does this happen?

Answer 4

Frameshift mutation; deletion or insertion of a number of nucleotides not divisible by 3 shifts the reading frame

Question 5

What kind of protein usually results from a frameshift mutation? Give an example of a disease resulting from this type of mutation.

Answer 5

A truncated and nonfunctional protein; Duchenne muscular dystrophy

Question 6

A lab detects a mutation: ACTCCTGAGGAG to ACTCCTGTGGAG. Protein size is unchanged; the protein is nonfunctional. Identify the mutation type.

Answer 6

This is likely a missense mutation (GAG to GTG = glutamate to valine)

Question 7

A mutation causes a guanine to replace an adenine. This is a ____ (transition/transversion).

Answer 7

Transition (purine to purine or pyrimidine to pyrimidine)

Question 8

A mutation causes a guanine to replace a thymine. This is a ____ (transition/transversion).

Answer 8

Transversion (purine to pyrimidine or vice versa)

Question 9

A patient tests positive for a hemoglobin-related disease caused by a missense mutation. What is the disease?

Answer 9

Sickle cell disease

Question 10

What happens to Escherichia coli in the absence of glucose and the presence of lactose?

Answer 10

The lac operon is activated; a switch to lactose metabolism occurs

Question 11

Lac operon genes are strongly expressed when there is a ____ (high/low) level of glucose and lactose is ____ (available/unavailable).

Answer 11

Low; available

Question 12

Escherichia coli is grown in the lab. Are lac operon genes strongly or not strongly expressed in case of low glucose and available lactose?

Answer 12

Strongly expressed.

Question 13

Are lac operon genes strongly or not strongly expressed in case of low glucose and low lactose? How about high glucose and low lactose?

Answer 13

No, not expressed; no, not expressed. Very low basal expression

Question 14

During nucleotide excision DNA repair, which enzyme removes the damaged DNA?

Answer 14

Endonuclease

Question 15

A 2-y/o child must stay inside during the day because sunlight causes dry skin and sunburn. By what mechanism does this disease work?

Answer 15

A defect in nucleotide excision repair that prevents repair of thymidine dimers (xeroderma pigmentosum)

Question 16

What is the first step in the base excision repair of damaged DNA?

Answer 16

Glycosylases recognize and remove a single damaged base

Question 17

In base excision repair, what do the apurinic/apyrimidinic endonucleases do?

Answer 17

They cut the DNA at apurinic and apyrimidinic sites and remove the empty sugar

Question 18

In single-strand DNA repair, how do nucleotide excision and base excision repair differ?

Answer 18

Nucleotide excision removes the entire nucleotide structure, and base excision repair removes bases without disturbing the DNA backbone

Question 19

What type of DNA repair is important in spontaneous/toxic deamination?

Answer 19

Base excision repair

Question 20

A patient lacks the ability to carry out nonhomologous end joining in DNA. What disease does the patient have?

Answer 20

Ataxia telangiectasia, a failure of nonhomologous end joining (bringing together of DNA fragment ends to repair double-stranded breaks)

Question 21

Which method of DNA repair repairs double-stranded breaks? What two conditions are associated with it?

Answer 21

Nonhomologous end joining; ataxia telangiectasia and Fanconi anemia

Question 22

A patient is found to have hereditary nonpolyposis colorectal cancer (HNPCC). What process is defective? How does it occur normally?

Answer 22

Mismatch repair; recognition of newly synthesized strand, removal of mismatched nucleotides, and filling and resealing of the gap

Question 23

A patient has xeroderma pigmentosum. What process is defective? How does this process occur normally?

Answer 23

Nucleotide excision repair; specific endonucleases release damaged bases, and DNA polymerase and ligase fill and reseal the gap

Question 24

How does the process of repair of spontaneous/toxic deamination work normally?

Answer 24

Nucleotide removal (5′-end cleaved), lyase cleaving of 3′-end, gap filling with DNA polymerase-β, sealing with DNA ligase

Question 25

In what direction does protein synthesis proceed?

Answer 25

From N-terminus to C-terminus

Question 26

DNA and RNA are synthesized in the ____–to–____ direction; mRNA is read in the ____to–____ direction.

Answer 26

5′ 3′; 5′ 3′

Question 27

A new drug that blocks DNA replication has been given to a patient. What is most likely modified in the chemical structure of the drug?

Answer 27

3′-OH, preventing the addition of the next nucleotide (chain termination) by way of the triphosphate bond

Question 28

For which amino acid does the initial AUG code in prokaryotes? What about in eukaryotes?

Answer 28

Formylmethionine in prokaryotes; methionine in eukaryotes

Question 29

What codon is the mRNA start codon? What amino acid does it code for?

Answer 29

AUG (or rarely, GUG); methionine (AUG inAUGurates protein synthesis)

Question 30

What are the three stop codons?

Answer 30

UGA, UAA, and UAG (UGA = U Go Away, UAA = U Are Away, & and UAG = U Are Gone)

Question 31

An experimental new drug blocks the removal of methionine before translation has finished in eukaryotic cells. Could this cause problems?

Answer 31

Yes, because methionine is sometimes removed from the developing protein before translation is completed

Question 32

An experimental drug increases the level of N-formylmethionine (fMet) within prokaryotic cells. What is the result?

Answer 32

Stimulation of neutrophil chemotaxis by fMet

Question 33

Organize these from 3′ to 5′ of a template strand: termination signals, promoter, enhancer, transcribed region

Answer 33

Enhancer, promoter, transcribed region, termination signals—opposite for the coding strand

Question 34

Where is the TATA box found?

Answer 34

In the promoter region

Question 35

What does the transcribed region consists of?

Answer 35

Introns and exons

Question 36

What is the name of the DNA site at which RNA polymerase and transcription factors bind?

Answer 36

Promoter

Question 37

What elements make up the promoter region?

Answer 37

An AT-rich sequence with TATA and CAAT boxes

Question 38

The promoter is ____ (upstream/downstream) of its gene locus

Answer 38

Upstream

Question 39

What is the name for a DNA site where negative regulators (repressors) bind?

Answer 39

Silencer

Question 40

What is the name for a stretch of DNA that alters gene expression by binding transcription factors?

Answer 40

Enhancer

Question 41

Where might enhancers and silencers be located relative to the gene being regulated?

Answer 41

Far from, close to, or within the gene itself